awful noise

Ex mother in law gave me her 93 olds 88,bought a new battery,checked all fluids,cranked it up,idled real high,went to turn engine off,and heard a awful noise under hood,sort-of "knock". Not real loud,but I heard it,Called her to see if she has heard any type of noise,she said no,then informed me that it sat up for about 5 months,I'm to scared to crank it again.Any help would be outstanding,i figured the high idleing was vacum line

Did it knock after you turned off the key? Did it continue running for a bit?

No,It knocked as it shut off,hard to explain,but i'm thinking the high rpms had something to do with it

hmm, that's odd.. It could have some dry rotted vacuum lines. Is the fuel fresh?

NO,guess I need to drain whats left in the tank huh? will get back to ya after troubleshooting a day or two

Should i replace All the vacum lines?

Just go thru them all and squeeze them. A good vacuum hose will feel firm and flexible. Mushy or hard is bad. Also any hose that turns your fingers black after squeezing it needs replaced.

ok,thx so much for the help